The present invention relates to a dual selection system for a reference frequency for use in a clock, and more particularly to a reference frequency dual selection system for a clock which can use an oscillation signal of a clock oscillation circuit as a reference signal during a long-term back-up and can use an oscillation signal of a system oscillation circuit as a reference signal during a short-term back-up.
Generally, in audio and video appliances which utilize a microcomputer, a time-indicating function is provided. To carry out the time-indicating function in such appliances, a reference frequency of 32.768 KHz for driving a clock has been required.
Accordingly, a clock oscillation circuit has been required to produce a reference frequency for driving the clock and a system oscillation circuit has been required for the microcomputer and the like.
Thus, since such systems have the disadvantage in that they require an additional oscillation circuit for use in the clock, the whole circuit configuration of the system is complicated and also it uses an expensive component such as a crystal, thereby increasing the cost of product.